1. Field of the Invention
The present invention relates generally to navigation apparatuses and, more particularly, to a navigation apparatus in which a guide picture for guiding a motor vehicle to a destination is displayed on a display unit.
2. Description of the Related Art
A vehicle navigation apparatus of a well known type performs vehicle travel guidance, enabling a driver to easily drive the vehicle to a desired destination. The navigation apparatus detects the position of the vehicle, reads out map data pertaining to an area at the vehicle position from e.g. a CD-ROM (compact disk read-only memory), and displays a map image on a display screen while superposing a mark representing the position of the vehicle (user""s vehicle position mark) on a predetermined portion of the map image. As the present position of the vehicle changes with movement of the vehicle, the vehicle position mark in the image is moved or the map is scrolled while the vehicle position mark is fixed at a predetermined position, for example, at the center of the image, thereby enabling the driver to recognize the map information of the area at the vehicle position at a glance.
Such a navigation apparatus has a route guidance function for setting a guided route from a starting point to a destination and performing intersection guidance (displaying an enlarged intersection diagram and the direction in which a vehicle is to advance) while displaying the guided route on a map. When a starting point and a destination are input, a guide route control section of the navigation apparatus automatically determines a most suitable guided route and successively stores nodes (in terms of longitude and latitude) constituting the guided route in a memory. During actual traveling, the node series stored in the memory is searched for a portion of the guided route to be displayed on a map display area of the display screen and the portion of the guided route is displayed so as to be discriminable from other routes. When the vehicle is within a predetermined distance of and approaching an intersection, an intersection guidance diagram (an enlarged intersection diagram with an arrow indicating the direction in which the vehicle is to travel at the intersection) is displayed to inform the driver of the desired one of the roads or directions at the intersection. If the vehicle deviates from the guided route (off-route travel), the guided route is updated by recalculating a new route from the present vehicle position to the destination.
FIG. 17 is a diagram of an example of a guided route display containing a vehicle mark CM, a guided route RT (dotted line) and an enlarged intersection diagram EL1 of an intersection Q. The enlarged intersection diagram EL1 showing intersection formation links B1 to B4, represented by link figures having a predetermined width, is converted into a perspective view (as shown) before being displayed. Each link is displayed with a name of a place to which a corresponding route leads (OHMIYA, TOKOROZAWA, URAWA STATION, NIHONBASHI). An arrow ARR is also displayed to indicate the direction in which the guided route leads to the destination. To draw such an enlarged intersection diagram as shown in FIG. 18, an area through 360xc2x0 about the intersection Q is divided into eight equal sections symmetrical about the direction of entry into the intersection (the direction of an intersection entry link L1), thereby obtaining eight angular ranges (reverse-to-entry-direction range A1, off-to-lower-left range A2, left turn range A3, off-to-upper-left range A4, straight drive range A5, off-to-upper-right range A6, right turn range A7, off-to-lower-right range A8). Then the relationship between intersection formation links and the angular ranges is examined to determine the angular ranges within which the intersection formation links fall, and an enlarged intersection diagram is formed and drawn in which the entry and diverging links extend in directions corresponding to the angular ranges within which the intersection formation links fall.
FIG. 19 is a table showing spoken intersection guidance sentences of the navigation apparatus. If the direction of an exit link corresponds to the right turn direction, spoken guidance such as xe2x80x9cTurn right at the next intersectionxe2x80x9d is given. If the direction of an exit link corresponds to the off-to-upper-right direction, spoken guidance such as xe2x80x9cTurn off to the right at the next intersectionxe2x80x9d is given. In some navigation systems, intersection guidance is not performed when driving straight through the intersection.
The vehicle navigation apparatus described above corresponds to those of the type commonly used in Japan. A vehicle navigation apparatus representative of the type commonly used in U.S.A. is arranged to display guidance pictures such as those shown in FIGS. 20A to 20F, without displaying a map picture showing a map and a vehicle position mark during vehicle traveling, and to guide a driver by using spoken information for designating the direction in which to drive. In each of the guidance pictures shown in FIGS. 20A to 20F, the distance (in miles) to an intersection is indicated in a space CDS; the distance (in miles) to a destination is indicated in a space DDS; sign VCD indicates a state of providing spoken guidance; the present time is displayed in a space TDL; and a heading direction is indicated in a guidance image NVG. If there is no intersection or a branching point in a guided route within a predetermined distance of the present vehicle position, a guidance picture such as FIG. 20A designating straight travel is displayed. If there is an intersection being approached within the predetermined distance, a guidance picture such as one of FIGS. 20B to 20E is displayed which contains an enlarged diagram of the intersection or branching point and an arrow indicating a heading direction. Where a U-turn is required, a U-turn figure as shown in FIG. 20F is displayed. When a point at a predetermined distance from the branching point or intersection is reached, spoken guidance is provided to designate a heading direction.
The navigation apparatus of the type used in the U.S.A. displays guidance pictures instead of map pictures during navigation, as described above. However, it detects the position of the vehicle, reads out map data corresponding to the vehicle position from a map data base such as a CD-ROM, displays, by using map data, an enlarged diagram of an approached intersection or a branching point, which may exist in a guide route in a predetermined distance range from the present vehicle position, along with an arrow indicating a heading direction in the same manner as the intersection enlarged diagram display in the Japanese type navigation apparatus, and performs speech guidance by designating the heading direction. The navigation apparatus displays a guidance picture indicating driving straight if there is no branching point or intersection being approached within the predetermined distance.
If the navigated vehicles moves off of the guided route (off-route travel), the navigation apparatus updates the guided route by recalculating a new route from the present vehicle position to the destination. Further, at the time of guided route setting, the display changes to show a map picture, thereby enabling a starting point and a destination to be input for guided route setting.
As described above, the navigation apparatuses of the types in Japan and U.S.A. have generally the same internal configurations. Reduced to essentials, they differ only in display picture control.
The vehicle position is measured by self-contained navigation sensors (a distance sensor and a bearing sensor) mounted in the vehicle (self-contained navigation) or by a global positioning system (GPS) including a satellite (satellite navigation). Vehicle position measurement based on self-contained navigation can be performed at a comparatively low cost but entails the problem of sensor errors reducing the measuring accuracy, and therefore requires correction processing such as map matching processing. Satellite navigation enables absolute-position detection. However, measured position data obtained by satellite navigation includes drift position errors resulting from various causes. The nominal accuracy of the U.S. GPS system is 100 m or less (95% of the time). Satellite navigation also entails the problem of position detection failure in e.g. a tunnel or a building where the satellite radio signals are obstructed.
Vehicle navigation apparatuses using both self-contained navigation and satellite navigation have recently been developed to avoid these problems. In such navigation apparatuses, the position and bearing are dead-reckoned by self-contained navigation in an ordinary situation, and the dead-reckoned vehicle position is corrected by map matching processing to determine the actual vehicle position on a traveled road. If the navigation apparatus is disabled from map matching by some cause with the result that the vehicle position measured by self-contained navigation deviates from the actual vehicle position so that the distance between the vehicle position measured by self-contained navigation and vehicle position measured by the GPS exceeds an error range of the GPS, then the position measured by the GPS is used as a corrected vehicle position, to find the traveled road by map matching processing, thereby determining the actual vehicle position.
In self-contained navigation, the vehicle position is detected by integration of output signals from a distance sensor and a relative direction sensor, as described below. FIG. 21 is a diagram of a vehicle position detection method using self-contained navigation. The distance sensor is assumed to output a pulse each time a unit distance L0 is traveled by the vehicle. A reference bearing (xcex8=0) corresponding to the plus direction of X-axis is set, and the direction of anticlockwise rotation from the reference bearing is assumed to be a plus direction. If a preceding vehicle position is represented by a point P0 (X0, Y0); an absolute bearing of a vehicle heading at the point P0 is xcex80; and an output from the relative bearing sensor when the unit distance L0 is traveled is xcex94xcex81, a change in the vehicle position is represented by
xcex94X=L0xc2x7cos(xcex80+xcex94xcex81)
xe2x80x83xcex94Y=L0xc2x7sin(xcex80+xcex94xcex81)
A dead-reckoned bearing xcex81 of the vehicle heading direction and a dead-reckoned vehicle position (X1, Y1) at a present point P1 can be calculated by vector addition expressed by the following equations:
xcex81=xcex80+xcex94xcex81xe2x80x83xe2x80x83(1)
X1=X0+xcex94X=X0+L0xc2x7cosxcex81xe2x80x83xe2x80x83(2)
Y1=Y0+xcex94Y=Y0+L0xc2x7sinxcex81xe2x80x83xe2x80x83(3)
Accordingly, if the absolute bearing and the position coordinates at a starting point are given, the vehicle position can be detected (dead-reckoned) in a real time manner by repeating the calculation of equations (1) to (3) each time the vehicle moves through the unit distance.
In self-contained navigation, however, errors are accumulated during traveling, so that the dead-reckoned position deviates from the traveled road. Therefore, the dead-reckoned vehicle position is collated with road data by map matching processing to be corrected to the actual vehicle position on the road. FIGS. 22 and 23 are diagrams explaining map matching based on a projection method. It is assumed here that the present vehicle position is at a point Pixe2x88x921(Xixe2x88x921, Yixe2x88x921), and that the vehicle heading direction is xcex8ixe2x88x921 (FIG. 22 shows a case where the point Pixe2x88x921 does not coincide with a road RDa.) If a relative bearing when a certain distance L0 (e.g. 10 m) is traveled from the point Pixe2x88x921 is xcex94xcex8i, a vehicle position Pixe2x80x2(Xixe2x80x2, Yixe2x80x2) dead-reckoned by self-contained navigation and a dead-reckoned bearing xcex8i at Pixe2x80x2 are obtained by the following equations:
xcex8i=xcex8ixe2x88x921+xcex8ixe2x88x921
Xixe2x80x2=Xixe2x88x921+L0xc2x7sinxcex8i
Yixe2x80x2=Yixe2x88x921+L0xc2x7sinxcex81
In this situation, (a) road data is searched for a link (an element constituting a road) which is contained in a 200 m square area surrounding the dead-reckoned vehicle position Pixe2x80x2, to which a perpendicular having a length not larger than a certain distance (e.g., 100 m) can be drawn from the dead-reckoned vehicle position Pixe2x80x2, and which is at an angle not larger than a certain value (e.g. 45xc2x0) from the dead-reckoned vehicle bearing xcex8i at the dead-reckoned position Pixe2x80x2. In this case, a link LKa1 of a bearing xcex8a1 on the road RDa (straight line connecting nodes Na0 and Na1) and a link LKb1 of a bearing xcex8b1 on a road RDb (straight line connecting nodes Nb0 and Nb1) are searched out as such a link. (b) Then the lengths of perpendiculars RLia and RLib drawn from the dead-reckoned vehicle position Pixe2x80x2 to the links LKa1 and LKb1 are obtained. (c) Thereafter, a coefficient Z is calculated by the following equations:
Z=dLxc2x720+dxcex8xc2x720(dxcex8xe2x89xa635xc2x0)xe2x80x83xe2x80x83(4)
Z=dLxc2x720+dxcex8xc2x740(dxcex8 greater than 35xc2x0)xe2x80x83xe2x80x83(4)xe2x80x2
where dL is the length of the perpendicular drawn from the dead-reckoned vehicle position Pixe2x80x2 to each link (the distance between the dead-reckoned vehicle position and the link) and dxcex8 is the angle between the dead-reckoned vehicle bearing xcex8i and the link. A larger weighting function is used when the angle dxcex8 is large.
(d) After the coefficient value Z has been obtained, some of the links satisfying the following conditions 1, 2, and 3,:
1) Distance dLxe2x89xa675 m (=maximum absorbable distance),
2) Angular difference dxcex8xe2x89xa630xc2x0 (=maximum absorbable angle),
3) Coefficient value Zxe2x89xa61500 are obtained and the one having the smallest coefficient value in the links satisfying these conditions, i.e. link LKa1 in this case, is set as a matching candidate (most probable road). (e) Then a travel locus SHi connecting the points Pixe2x88x921 and Pixe2x80x2 is translated in a direction along the perpendicular RLia until the point Pixe2x88x921 comes onto the link LKa1 (or an extension of the link LKa1) to obtain translated points PTixe2x88x921 and PTixe2x80x2 of the points Pixe2x88x921 and Pixe2x80x2 (f) Finally, the travel locus SHi is rotated on the point PTixe2x88x921 until the point PTixe2x80x2 comes onto the link LKa1 (or an extension of the link LKa1) to obtain a moved point of the point PTixe2x80x2, which is set as an actual vehicle position Pi (Xi, Yi). The bearing xcex8i is preserved as the vehicle heading at the actual vehicle position Pi. In a case where the point Pixe2x88x921 representing the preceding vehicle position is on the road RDa, the translated point PTixe2x88x921 coincides with the point Pixe2x88x921, as shown in FIG. 23.
A situation described below may be taken into consideration, especially in the U.S.A. and geographically similar countries. As shown in FIG. 24, a convenience store SHP1 and other stores SHPi (i=2, 3 . . . ) are all located in a large-area site, a large parking area PKA is located in front of the stores, and roads RD1 to RD4 stored in the map data base surround the parking area PKA. The roads RD1 to RD4 are at a short distance from the parking area PKA. The parking area PKA is not stored in the map data base (i.e., is off the road net). If a vehicle CR having the navigation apparatus enters the parking area PKA, the vehicle position is erroneously determined to be on the adjacent road RD1 by the map matching processing, resulting in an error in position correction. Thereafter, the navigation apparatus cannot recognize the correct vehicle position and cannot make an appropriate guidance picture display or spoken guidance when the vehicle moves out of the parking area PKA back onto a road on a guided route.
In a situation where a guided route is set as indicated by hatching in FIG. 25, if the vehicle position is determined to be on the road RD1 adjacent to the parking area PKA by the map matching processing to cause an erroneous position correction, then an off-route movement is recognized, a guided route recalculation is performed to newly set guided route NVRT indicated by the double-dot-dash line, and a guidance picture display and spoken guidance which are inappropriate or irrelevant are provided. For example, in a case where the vehicle CR is travelling leftward through a point Pa, a correct guidance picture such as that shown in FIG. 26A designating a right turn 500 m ahead is displayed. In such a situation, if the vehicle enters the parking area PKA and if the vehicle position is erroneously corrected to a point on the road RD1 by map matching, then recalculation of guided route NVRT is performed as mentioned above to display an incorrect guidance picture, such as that shown in FIG. 26B designating a left turn 100 m ahead. Then, if the vehicle makes a U-turn in the parking area PK4 as indicated by the broken line, it is erroneously determined that the vehicle has U-turned on the road RD1 and a guidance picture as shown in FIG. 26C designating a U-turn is displayed. If the vehicle returns to the road RD2, guided route recalculation is performed, the first guided route (hatching) is obtained and a guidance picture such as that shown in FIG. 26D designating a right turn 200 m ahead is displayed.
As described above, if the vehicle enters an area other than on the roads (i.e. not in the map data base), e.g. a parking lot, grounds of a facility or factory, a park or a campus, the selection of guidance pictures and spoken guidance becomes incorrect during movement in the off-road area, so that the driver has a feeling of uncertainty in terms of guidance. Even after the vehicle exits the off-road area, there is a possibility of the navigation apparatus performing erroneous position correction to lose the vehicle position, resulting in failure to display a correct guidance picture or to give correct spoken guidance.
A navigation apparatus in accordance with this invention does not output an inappropriate or irrelevant guidance picture display or spoken guidance, even when the navigated vehicle enters an area other than on the roads in the map data base, e.g., a parking lot, factory or facility grounds, a park or a campus.
The present navigation apparatus also displays a correct guidance picture and performs correct speech guidance for navigating the vehicle to a destination when the vehicle exits such an area (an xe2x80x9coff-road net areaxe2x80x9d).
According to one aspect of the present invention, a navigation apparatus includes a map data base for storing map data, a detector for detecting an entry of a vehicle into such an area other than roads stored in the map data base, and a display control for changing a guidance picture to a map picture showing a map image surrounding the vehicle position and a vehicle position mark when the vehicle enters the off-road net area.
In this navigation apparatus, when the vehicle enters such an off-road net area, the guidance picture is changed to a map picture to avoid outputting an erroneous guidance picture display or guidance speech, so that the driver has no feeling of uncertainty. Also, a detector for detecting an exit from such an area is provided to change the map picture to the guidance picture when the vehicle exits the area, thereby providing a guidance picture display and spoken guidance for navigation to a destination after exiting from the area.
According to another aspect of the present invention, a navigation apparatus includes a map data base for storing map data, a vehicle position corrector for obtaining, by map matching processing, a most probable candidate road satisfying a predetermined condition for correcting the position of the vehicle to a point on the most probable candidate road, and for thereafter continuing the map matching processing each time a predetermined distance is traveled, a detector for detecting an entry of the vehicle into an off-road net area, and a display control for changing a guidance picture to a map picture showing a map image about the vehicle position and a vehicle position mark when the vehicle enters the area, wherein correcting the position by the map matching processing stops when the vehicle enters the area.
In this navigation apparatus, when the vehicle enters such an area, a guidance picture is changed to a map picture and correcting the vehicle position by map matching stops, thereby avoiding occurrence of erroneous position correction to a position on a road adjacent to the area. Therefore, the possibility of providing an erroneous guidance picture display or spoken guidance is eliminated, so that the driver has no feeling of uncertainty.
A detector for detecting an exit from such an area is also provided to restart correcting the vehicle position by map matching and to change the map picture for a guidance picture when the vehicle exits the area. Even after exiting from the area, this navigation apparatus can recognize the vehicle position with a certain error, such that the vehicle position can be corrected by the restated map matching processing. Also, a correct guidance picture display and a correct spoken guidance to the desired destination can be output.
According to still another aspect of the present invention, a navigation apparatus includes a map data base for storing map data, a vehicle position corrector for obtaining, by map matching processing, a most probable candidate road satisfying a predetermined condition, for correcting the position of a vehicle to a point on the most probable candidate road, and for thereafter continuing the map matching processing each time a predetermined distance is traveled, a route calculator for calculating a guide route from the present vehicle position of a vehicle to a destination when the vehicle deviates from a destination previously set, a detector for detecting an entry of the vehicle into an off-road net area, and a display control for changing a guidance picture to a map picture showing a map image surrounding the vehicle position and a vehicle position mark when the vehicle enters the area, wherein, when the vehicle enters the area, the vehicle position correction means stops correcting the position by the map matching processing and the guided route calculator stops calculating the guided route.
In this navigation apparatus, when the vehicle enters the above-mentioned area, a guidance picture is changed to a map picture, correcting the vehicle position by map matching stops and recalculating a guided route is also stopped, thereby avoiding occurrence of erroneous position correction to a position on a road adjacent to the area, while recalculation of a guided route in response to being off-route is inhibited. Therefore the possibility of providing an erroneous guidance picture display or spoken guidance is eliminated, so that the driver has no feeling of uncertainty.
Also, a detector for detecting an exit from such an area is provided to restart correcting the vehicle position by map matching and recalculating a guide route when the vehicle exits the area. Even after the exit from the area, this navigation apparatus can recognize the vehicle position with a certain error, such that the vehicle position can be corrected by the restarted map matching processing. Also, a correct guidance picture display and a correct spoken guidance to the desired destination can be provided. Further, even if the vehicle exits from the area at a location different from the entrance, to travel on a road different from the previously set guided route, a new guided route is recalculated, to provide a correct guidance picture display and correct spoken guidance for navigation to the destination.